Would this be fine for a single Dell U2713HM ? I pulled the trigger and joined, it looks awesome. Also, Do I need to have this mounted on the side of my desk to center the display? Or can I have this arm mounted in the center and still be able to center the display itself?

The U2713HM is about 5 lbs under Erotech's limit for the arm, should work just fine. You can mount this thing anywhere you want on the edge of the desk and it will center with your desk as long as the two parts of the arm reach that point.